Ballasts are used in the artificial illumination arts for controlling power applied to lamps, such as fluorescent lamps. When such lamps are in use for extended lengths of time, thermionic emission materials coated on the lamp electrode, such as Barium, Strontium, etc. tend to be absorbed by the lamp tube walls, leaving the electrode coating depleted. When this electrode coating reaches a certain level, the voltage and current of the lamp become asymmetrical and once the coated material is completely depleted, the lamp can no longer be turned on. Partial depletion of the thermionic emission material, moreover, leads to increased electrode heating due to increased electrode resistance and a constant electrode current. In order to mitigate or avoid excess electrode heat, it is desirable to identify and replace lamps that are nearing the end of their service life prior to complete depletion of the electrode coating. However, a user typically cannot visually distinguish an end-of-life lamp from a good lamp. A need therefore exists for ballasts which facilitate the identification of end-of-life lamps.